1. Field of the Invention
The present disclosure relates to a display device, and more particularly, to a display device including a power supply unit that provides a compensation voltage.
2. Discussion of the Related Art
A liquid crystal display device displays an image by driving thin film transistors, formed on a substrate, according to input of image data.
The liquid crystal display device includes liquid crystal capacitors and storage capacitors, and displays an image by receiving voltages from a data driver and maintaining the voltages.
When the voltages having a predetermined polarity are continuously supplied, a common voltage is shifted in pixels of a panel of the liquid crystal display device. There is a smearing phenomenon on a screen, and thus the quality of the image is lowered. To prevent this, a compensation voltage for compensating the common voltage may be provided to the panel, which will be described hereinafter with reference to FIG. 1.
FIG. 1 is a circuit diagram of an exemplary display device according to the related art.
In FIG. 1, the display device according to the related art includes a panel 10 and a power supply unit 20.
The power supply unit 20 includes an operational amplifier 22, a common voltage supply section 23, a first capacitor C1, a first resistor R1 and a second resistor R2. An output (O) of the operational amplifier 22 is connected to the panel 10, and a non-inverting input (+) of the operational amplifier 22 is connected to the common voltage supply section 23. The first capacitor C1 and the first resistor R1 are connected between the panel 10 and an inverting input (−) of the operational amplifier 22 in series. The second resistor R2 is connected between the output (O) and the inverting input (−) of the operational amplifier 22.
A gate driver 15 and a data driver 16 are connected to the panel 10.
In the display device according to the related art, feedback is performed by transferring a panel common voltage PVcom through a circuit path between the panel 10 and the inverting input (−) of the operational amplifier 22, and a compensation voltage Vi generated according to the feedback performance is provided to panel 10.
The operational amplifier 22 outputting the compensation voltage Vi has a fixed compensation rate in order to reduce oscillations that may occur during the feedback performance. In this case, it is hard to perform compensation for each location and each size because of a common voltage shift, which non-linearly increases as time passes.
In addition, the display device according to the related art generates the compensation voltage Vi based on the panel common voltage PVcom. Namely, since the panel common voltage PVcom is measured and the compensation voltage Vi to the measured common voltage is outputted for the feedback, a shift to the panel common voltage may have occurred. Thus, the compensation voltage Vi is not applied at an appropriate timing.
Therefore, the panel 10 cannot suitably receive the compensation voltage Vi and cannot normally display an image. This will be described hereinafter with reference to FIG. 2.
FIG. 2 is a view of illustrating an upper portion and a lower portion of a photograph of an image displayed by a display device according to the related art.
As shown in FIG. 2, in the upper portion of the display device according to the related art, although the compensation voltage is applied, the common voltage shift occurring in the panel is not compensated, and thus patterns having a lattice shape are shown in an area A of the panel.
In the lower portion of the display device, the common voltage and the compensation voltage accord with each other as compared with the upper portion, and patterns like the upper portion are hardly shown.
This is why the common voltage shifts differ in the upper and lower portions. Thus, when the same compensation voltage is applied to the panel, the common voltage shift is sufficiently compensated in the lower portion while the common voltage shift is not sufficiently compensated in the upper portion.
Accordingly, in the display device according to the related art to which the compensation voltage having the same magnitude as the common voltage shift, the image quality is lowered. Additionally, since reproducibility and visibility differ in the upper and lower portions of the panel, the image quality of the display device is not uniform.